Problem 101 - Chemistry The Central Science

Question

Which statement correctly describes a difference between graphene and graphite? (a) Graphene is a molecule but graphite is not. (b) Graphene is a single sheet of carbon atoms and graphite contains many, and larger, sheets of carbon atoms. (c) Graphene is an insulator but graphite is a metal. (d) Graphite is pure carbon but graphene is not. (e) The carbons are \(s p^{2}\) hybridized in graphene but \(s p^{3}\) hybridized in graphite.

Step-by-Step Solution

Answer

The correct statement that describes the difference between graphene and graphite is (b): Graphene is a single sheet of carbon atoms and graphite contains many, and larger, sheets of carbon atoms.

Step 1: Statement A

Although both graphene and graphite are comprised of carbon atoms, they differ in their arrangement. Graphene can be considered as an individual layer, a giant molecule, but graphene is not a molecule. Hence, this statement is incorrect.

Step 2: Statement B

This statement is correct. Graphene is a single sheet of carbon atoms arranged in a hexagonal lattice, while graphite is composed of multiple layers of such sheets. The layers in graphite are held together by weak Van der Waals forces allowing them to slide easily over each other, which makes graphite a good lubricant and gives it its characteristic slippery feel.

Step 3: Statement C

Both graphene and graphite are conductive, but neither is considered a metal. Graphene exhibits high electron mobility and can function as an excellent conductor, while graphite is a good conductor of electricity in certain directions (due to its stacking of layers). Therefore, this statement is incorrect.

Step 4: Statement D

Both graphene and graphite are composed of pure carbon atoms. The difference lies in the arrangement of the carbon atoms, not in their chemical composition. Thus, this statement is incorrect.

Step 5: Statement E

In graphene, each carbon atom forms three covalent bonds with three other carbon atoms, resulting in an \(sp^2\) hybridization. In graphite, the situation is the same, with the carbon atoms also being \(sp^2\) hybridized. Therefore, this statement is incorrect. The correct statement that describes the difference between graphene and graphite is (b).

Key Concepts

Carbon Atom Structure

Carbon atoms are the fundamental building blocks of both graphene and graphite. Each carbon atom has six electrons, with the electronic configuration of 1s² 2s² 2p². This means that each carbon atom has two inner electrons "locked" in the 1s orbital and four "available" electrons in the second shell that are available for bonding.
Carbon's structure allows it to create various forms of bonding, leading to the creation of different carbon-based materials like diamond, graphene, and graphite.
In these structures, carbon atoms can form a variety of shapes and bonds. For instance:

• Graphene consists of carbon atoms arranged in a 2-dimensional, honeycomb lattice, where each carbon atom connects with three others.
• Graphite is a stack of graphene layers, each one bonded weakly to the one above and below by Van der Waals forces.

This unique arrangement gives these substances their distinctive properties, where atomic structure directly influences material behavior.

Hybridization in Carbon

Hybridization is a concept in chemistry that explains the mixing of atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds. Carbon, in its stable forms of diamond, graphite, or graphene, exhibits different types of hybridizations based on its bonding.

• In graphene, carbon atoms undergo { \(sp^2\) hybridization}. This means that each carbon atom forms three σ bonds using one s and two p orbitals, leaving one p orbital perpendicular to the plane. This remaining p orbital overlaps with another p orbital from a neighboring atom creating the π-bonding, which is crucial for conductivity.
• Despite the common misconception, graphite also uses \(sp^2\) hybridization. In graphite, carbon forms planar structures, and like graphene, it involves three adjacent atoms to form σ bonds, with remaining π bonds contributing to the overall stability of the layers.

Hence, the same type of hybridization occurs in both graphene and graphite, highlighting their similar bonding structure despite a difference in their macroscale architecture.

Conductivity of Carbon Materials

Conductivity refers to the capacity of a material to conduct electricity. In carbon materials, conductivity results from their structural arrangement and type of hybridization.

• Graphene is renowned for its extraordinary conductivity. Its structure, with delocalized π electrons freely moving within the plane, allows it to exhibit electron mobility that rivals traditional conductors like copper. This makes graphene an excellent material for electronic applications.
• Graphite, though less celebrated for conductivity compared to graphene, functions efficiently as a conductor too. Within its layered structure, the presence of π electrons enables electrical conduction parallel to the layers. Graphite's ability to conduct electricity is widely utilized in batteries and as electrodes.

It's important to note that while graphene conducts in a plane, graphite conducts parallel to the sheets. Both materials, however, leverage their structural conductivity for technological and industrial applications, driven by the availability of free-moving electrons in their systems.